Conventionally, the business-use radio communication industry employs superheterodyne systems as a signal receiving system. In addition, recently, direct conversion systems small in mounting area have been expected to meet needs for miniaturization and the like.
It is known that, in receivers using such direct conversion systems, a DC offset occurs on a baseband signal, whereby reception sensitivity is degraded. Thus, for example, there have been conventionally proposed methods such as DC offset attenuation using a high pass filter and DC offset attenuation particularly suitable to perform communication using an FM/FSK modulation system (e.g., see JP 2017-34545 A).